Photopolymerization of ethylenically unsaturated compounds through the use of novel azole photoinitiators

ABSTRACT

A PROCESS FOR PHOTOPOLYMERIZATION OF ETHYLENICALLY UNSATUREATED ORGANIC COMPOUNDS IS DESCRIBED WHICH COMPRISES IRRADIATING A COMPOSITION INCLUDING A PHOTOPOLYMERIZABLE ETHYLENICALLY UNSATURATED ORGANIC COMPOUND AND AS A PHOTOPOLYMERIZATION INITIATOR AN AZOLE COMPOUND HAVING THE FORMULA:   R3-C&lt;(-X-C(-R2)=C(-R1)-N=)   WHEREIN:   X IS OXYGEN, SULPHUR,-NH-OR A-NR-GROUP, WHEREIN R IS AN ALKYL GROUP OF 1 TO 4 CARBON ATOMS, OR BENZYL, EACH OF R1 AND R2 (SAME OR DIFFERENT) IS HYDROGEN, HALOGEN, AN ALKYL GROUP OF 1 TO 4 CARBON ATOMS, OR A PHENYL GROUP, AND R3 IS HYDROGEN, HALOGEN, AN ALKYL GROUP OF 1 TO 4 CARBON ATOMS, A PHENYL GROUP, A NAPHTHYL GROUP OR A STYRYL GROUP;   OR AN AZOLE COMPOUND WHICH COMPRISES AN IMIDAZOLE GROUP INCORPORATED IN A POLYMER COMPRISING RECURRING UNITS OF THE FORMULA:   -(CH2-CH(-IMIDAZOL-4-YL)

3,597,343 PHOTOPOLYMERIZATIUN 01F ETHYLENICALLY UNSATURATED CGM?UNDS THROUGH THE USE OF NOVEL AZOLE PHOTOINITHATORS Gerard Albert Delzenne, s-Gravenwezel, and Urbain Leopold Laridon, Wilrijk, Belgium, assignor to Gevaert- Agfa N.V., Mortsel, Belgium No Drawing. Filed Nov. 21, 1967, Ser. No. 684,611 (Ilaims priority, application Great Britain, Dec. 8, 1966, 55,095/ 66 Int. Cl. (308d 1/00; C08t 1/16 U.S. Cl. 204ll59.23 9 Claims ABSTRACT OF THE DISCLOSURE 1 A process for photopolymerization of ethylenically unsaturated organic compounds is described which comprises irradiating a composition including a photopolymerizable ethylenically unsaturated organic compound and as a photopolymerization initiator an azole compound having the formula:

wherein:

X is oxygen, sulphur, NH- or a NR group, wherein R is an alkyl group of 1 to 4 carbon atoms, or benzyl,

each of R and R (same or diiferent) is hydrogen, halogen, an alkyl group of 1 to 4 carbon atoms, or a phenyl group, and

R is hydrogen, halogen, an alkyl group of 1 to 4 carbon atoms, a phenyl group, a naphthyl group or a styryl p; i

or an azole compound which comprises an imidazole group incorporated in a polymer comprising recurring units of the formula:

by heat. Moreover, the use of light alone, unaided by other agents, requires very long exposure times in order to polymerise the monomer sufficiently. Furthermore, the low rate of polymerisation necessitates the use of extremly intense radiations such as those obtained from high intensity mercury vapour lamps or carbon arcs.

A lot of photopolymerisation initiators, which under the influence of actinic light increase the photopolymerisation rate, have already been described. A survey of such photopolymerisation initiators has been given by G. Delzenne in 'Industrie Chimique Belge, 24 (1959) 739-764.

An object of the present invention is to provide a new class of photopolymerisation intiators which can be activated by actinic light.

Another object of the present invention is to provide a new class of photopolymerisation initiators which require a short exposure to actinic light.

A further object is to provide a process whereby the photopolymerisation of ethylenically unsaturated organic compounds can be carried out at a practicable rate by visible light as well as by ultra-violet light.

Other objects will appear hereinafter.

According to the present invention a process is provided for the photopolymerisation of ethylenically unsaturated organic compounds, which process comprises irradiating with light of wavelengths ranging from 2500 to 7000 angstroms a composition comprising a photopolymerisable ethylenically unsaturated organic compound and as a photopolymerisation initiator an azole compound of the formula:

wherein: i

X represents an oxygen atom, a sulphur atom, the group --NH or the group NR wherein R represents an alkyl group of 1 to 4 carbon atoms or a benzyl group;

each of R and R (same or different) represents a hydrogen atom, a halogen atom, an alkyl group of 1 to 4 carbon atoms, a phenyl group including a substituted phenyl group; and

R represents a hydrogen atom, a halogen atom, an alkyl group of 1 to 4 carbon atoms, a phenyl group including a substituted phenyl group, a napht-hyl group, or a styryl group;

or wherein the azole compound is an imidazole group incorporated in a polymer comprising recurring units of the formula:

The quantity of azoles (oxazoles, imidazoles or thiazoles) or of polymeric imidazole to be used as photopolymerisation initiator will of course be dependent upon many variables including the particular initiator used, the wavelength of light employed, the irradiation time and the monomer or monomers present. Usually the amount of azole or of polymeric imidazole is within the range of 0.01 to by weight based on the monomeric material initially present. It is seldom necessary to employ more than 0.2. to 2% by weight to obtain a good polymerisation rate.

In the further description there will be understood under the term azoles not only oxazoles, imidazoles and thiazoles but also the polymeric imidazoles.

The ethylenically unsaturated organic compounds may be exposed to any source of radiation providing wavelengths in the range of 2500-7000 angstroms, preferably 25006000 angstroms and still more preferably in the wavelength region of 3000-4000 angstroms. Suitable light sources include carbon arcs, mercury vapour lamps, fluorescent lamps, argon glow lamps, photographic flood lamps and tungsten lamps. Moreover, ordinary daylight may be used too.

A considerable increase of the rate of polymerisation can also be obtained by adding activating dyes taken from the class of acridine, phenazine, and fluoresceine dyes, and more particularly photo-oxidation sensitizers, in a concentration of 0.001 to 0.1% by weight based on the monomeric material present.

The photopolymerisation can be carried out by any of the well-known processes, such as bulk, emulsion, suspension and solution polymerisation processes. In all of these processes, the addition of an azole according to the invention to polymerisable materials subjected to the action of actinic light greatly increases the rate of photopolymerisation.

A base or support may be coated with a solution of the ethylenically unsaturated organic compound in a solvent therefor, this solution containing in dissolved state or homogeneously dispersed therein a photopolymerisation-initiating azole compound, whereupon the sol vent or solvent mixture is eliminated by known means such as evaporation, leaving a more or less thin coating of the ethylenically unsaturated organic compound on the base or support. Thereafter the dried photopolymerisable coating is exposed to actinic light rays.

When exposing the photopolymerisable composition to actinic light rays the polymerisation does not start immediately. Only after a short period, which among others depends on the ethylenically unsaturated organic composition, the photopolymerisation initiator and the lightintensity used, the photopolymerisation starts. The period necessary for obtaining a perceptible amount of polymerisation is a measure of the efliciency of the photopolymerisation initiator, and is named the inhibition period.

In some circumstances it may be desirable that the photopolymerisable composition comprises a hydrophilic or hydrophobic colloid as carrier or binding agent for the ethylenically unsaturated organic compound and the photopolymerization initiating azole compound. By the presence of this binding agent the properties of the lightsensitive layer are of course highly influenced. The choice of the binding agent is dependent on its solubility in solvents, which can also be used as solvents for the ethylenically unsaturated organic compounds and for the azole compound of the invention. Such binding agents are for instance poly(styrene), poly(methyl methacrylate), poly(vinyl acetate), poly(vinylbutyral), partially saponified cellulose acetate and other polymers that are soluble in solvents for initiators and monomers. In some instances water-soluble polymers can be used such as gelatin, casein, starch, carboxymethyl-cellulose and poly (vinyl alcohol). It is evident that the ratio of photo polymerisable composition to binding agent also influences the photopolymerisation. The larger this ratio, the higher the photopolymerisation rate generally will be for one and the same ethylenically unsaturated organic compound.

If the photopolymerisable composition is water-soluble water may be used as solvent for coating the support.

0n the contrary, if water-insoluble photopolymerisable compositions are used, organic solvents, mixtures of organic solvents or mixtures of organic solvents and water may be used.

Examples of suitable azole compounds are:

2,5-diphenyl-oxazole 2,5-diphenyl-4-methyl-oxazole 2,4,5-triphenyl-oxazole 2-styryl-5-phenyl-oxazole 2-(1-naphthyl)-5-phenyl oxazole imidazole 4,5-diphenyl-imidazole 2,4,5-triphenyl-imidazole (Iophine) 2-methyl-4,5-diphenyl-imidaz0le 2,4,S-trimethyl-imidazole 2,4,5-tribromoimidazole 4,5-bis(p-methoxyphenyl)-imidazole 2,4,S-triphenyl-N-methyl-imidazole N-benzyl-imidazole 2,4,S-triphenyl-thiazole.

The polymeric imidazoles, which are suitable as polymerisation initiators according to the invention, are polymers comprising a substantial amount of recurring units deriving from 4-vinyl-imidazole such as a copolymer of methyl methacrylate and 4-vinyl-imidazole.

Among these azoles the oxazoles can be obtained either by dehydration of the corresponding acylamino derivatives with phosphorus pentachloride or with sulfuric acid, or by reduction of the corresponding oxido-oxazoles synthesized by condensation of 1,2-diketomonoxime with aldehydes. Both methods are summarized in Chemical Reviews 37, 401 (1945).

A general synthesis for imidazole derivatives is the condensation of 1,2-dicarbonyl compounds with ammonia and an aldehyde. N-methyl imidazoles were obtained from the corresponding quaternized oxazoles by treating them with ammonium acetate and acetic acid under refluxing, whereas N-benzyl imidazole was obtained by reacting imidazole with benzylchloride.

The thiazoles are readily obtained either by condensation of thioamides with a-halogenated aldehydes or ketones, or by treating aminoaldehydes, aminoketones or aminoacid esters with phosphorus pentasulfide.

The process of the invention is applied to the photopolymerisation of compositions comprising ethylenically unsaturated organic compounds. These compositions may comprise one or more ethylenically unsaturated polymerisable compounds such as styrene, acrylamide, methacrylamide, methyl methacrylate and acrylonitrile. When two of these monomers are used in the same photopolymerisable composition or if they are mixed with other polymerisable compounds, copolymers are formed during the photopolymerisation. It is further presumed that in the case where the photopolymerisable material is used together with a polymeric binding agent, graft copolymers are formed between the polymeric binder and the photopolymerised material.

The photopolymerisable composition may also comprise or consist of unsaturated compounds having more than one carbon-to-carbon double bond, e.g. two terminal vinyl groups, or of a polymeric compound having ethlylenic unsaturation. During polymerisation of these compositions usually cross-linking will occur by means of the plurally unsaturated compound. Examples of compounds containing more than one carbon-to-carbon double bond, are, e.g., divinylbenzene, diglycol diacrylates and N,N'-alkylene-bis-acrylarnides. Examples of polymeric compounds containing ethylenically unsaturation are, e.g. allyl esters of polyacrylic acid, maleic esters of polyvinyl alcohol, polyhydrocarbons still containing carbon-to-carbon double bonds, unsaturated polyesters, cellulose acetomaleates, and allyl cellulose.

In the photopolymerization of ethylenically unsaturated compounds with azoles of the invention high temperatures are not needed. The exposure, however, to strong light sources at a relatively short distance, brings about a certain heating of the mass to be polymerised,

The image-wise photopolymerisation can also induce differential softening properties to the layer. This makes possible a reproduction process by material transfer when the image-wise photopolymerised layer is subsequently warmed up and pressed against a receiving sheet, so that which heating exercises a favourable influence upon the 5 the softened areas are transferred to the receiving sheet. polymerisation rate. The following examples illustrate the present inven- The products of the invention are useful as adhesives, tion. coating and impregnating agents, safety glass interlayers, etc. When photopolymerisation of the compositions is EXAMPLE 1 carried out within a mold, optical articles such as lenses 1O can be obtained A series of amounts of 3 g. of acrylamide was dis- The photopolyrnerisable compositions which contain Solved as y qhahtltles Of a f ces of azoles according to the invention are useful in the prep Water and 0f e y y h t0 W h1eh lhltlatlhg aration of photographic images. In this respect the presegehts had been d d 1 1 a mole/htre concentraent invention also comprises spreading the polymeris-able Then the sohltlohs Obtalhed e Poured Into ehemlcomposition upon a surface such as a surface of metal Cally and heat-feslsteht glass T e f th s and printing a design thereon photographically by exglass tubes an amount of photo-oxidatlon sensitlzer corposure to light through a suitable image pattern. Hereby fespohdfng Wlth 10-4 /hi as lndlcated in Table I the light induces polymerisation in the exposed areas of below 15 f Exposure Occurred Wlth a -C l d the photopolymerisation composition whereby the poly- 300 Watt hlgh Pressure mercury Vapour p Placed meric layer is rendered insoluble in the solvent or sola dlstahee 0t 18 After exposure each SOhItlOn Was vents used for applying the photopolymerisable layer. Phh lhto methanol whereby the Polymer termed P Thereafter the non-exposed areas are washed away with clPltatede each p y Separated, uu a solvent for the monomeric material. In this way printr dnedbahd Welghed- The Polht whleh the P y Could ing plates and photographic resist images are manufac- 20 sepiltated y g t l l the tlahle hl f g otured, which can be further used as planographic printf: gs y jggg'r ezg liz g fl le gx o'g urpe tz s gs artg shosm in ing plates, as matrices for printing matter, as screens for Table if P silk screen printing, and as photoresists for etching.

TABLE I Exposure Yield of time in polymer in Test Initiator Photo-oxidation sensitizer min. percent 5 15 2. 5 1 I. 2,4,5-trlphenyloxazole 45 23 s 60 33. 75 48 15 7 2 .110 Rose bengale 5 2 60 1) 15 8.7 3 d0 Euflavinc 30 36 5 45 i 15 5 19,5 4 2-(1maphthyl)-5-phenyl0xaz0le 5 37. 5 60 43, 5 75 64 15 6.7

5 ..d0 .l Rose bengale 60 m 2.2 6 2,5-diphenyl-4-1nethyloxaz0le 7.3 9.9 15 3.7 t 10.7 R 1 17.4 7 do ose )enga e 60 24 75 30 1g 4.3

1 8 2,5diphenyloxazole 2 60 15 4.1 20 1 10 e M 5 s. 1 9 styiyl 5 phenyloxazole do 60 27. 7 75 33.3 2-0-chl0r0phenyl-5-ph enyloxazole do 60 62 2-p-Inethoxyphenyl-fi-phenyloxazole. 60 57 2-p-nitrophenyl-5-phenyloxazole 60 30 1 2-rn-nitrophenyl-fi-phenyloxazole do 28 2g l 13.1 14 2,4,5-tnphenylnmdazole (Ioplnne) 240 3 300 87.5 5 8.45 15 2,4,5-triphenylimidazole Rose bengale 5 2. 45 10 13.8 6 10 Erythrosine 15 42 7 20 E 20 l 7 d0 Eoslne 1 13.1 20 58.5 8 "do Sahamne T (01.50240) (l) 45 34.2 60 42 19 .110 Benzoflavlne BFX (CI. 75 60 46.065). 90

TABLE I. Continned Exposure Yield of time in polymer in Test Initiator Photo-oxidation sensitizer min. percent 5 3. 57 11.7 20 4,5-diphenylimidazole Rose bengale 15.7 30 35. 2 10 30 7. 35 21 Imidazole d0 45 24.4 60

5 3. 5 22 N-Methyl-2,4,fi-triphenylimidazole ..do g 2 15 6. 7 23 N-Benzylimidazoledo 30 24. 2 5 24 2,4,5-triphenylthiazole do 28 EXAMPLE 2 imidazole units prepared similarly to the procedure de- TABLE II Exposure Yield of time in polymer in Test min. percent EXAMPLE 3 In chemically and heat-resistant glass tubes are placed a solution of 3 g, of acrylamide in a mixture of 5 ccs. of water and 5 ccs. of methylglycol, 10- mole/litre of an imidazole as listed below as an initiator, and l0- mole/ litre of rose bengale as a photo-oxidation sensitizer. Then the solutions are exposed by means of a high-pressure mercury vapour lamp of 80 Watt placed at 12 cm. Thereafter the polymer formed is precipitated by adding an excess of methanol, and separated.

scribed by Overberger and Vorchheimer (J. Am. Chem. Soc. 85, 951, 1963) are dissolved in a mixture of 5 ccs. of glycolmethylether and 5 ccs. of water, together with 3 g. of acrylamide and 1 mg. of rose bengale.

The solution obtained is exposed for 10 minutes by means of a high pressure mercury vapour lamp of 80 watt, at a distance of 12 cm. whereafter the precipitated polymer is separated and dried. Yield of polymer: 54%.

We claim:

1. Process for the photopolymerisation of ethylenically unsaturated organic compounds, which comprises irradiating with light of wavelengths ranging from 2500 to 7000 angstroms a composition comprising a photopolymerisable ethylenically unsaturated organic compound and as a photopolymerisation initiator (1) an azole compound of the general formula:

wherein X is oxygen, sulphur, -NH or a NR group, wherein R is an alkyl group of 1 to 4 carbon atoms, or benzyl,

each of R and R (same or diiferent) is hydrogen, halogen, an alkyl group of l to 4 carbon atoms, or a phenyl group, and

TABLE III Exposure Yield of time in polymer in Test Initiator Sensitizer min. percent 26 4,5-dipheny1-2-methylimidazole Rose bengale. 10 13. 3 27 2,4,5-tribrornoirnidazole .do 15 15 28 2,4,5-trimethylimidazole 15 11. 7 29- 4,5bis (p methoxyphenyl) imidazole 18 45 30- 2-m-nitrophenyl-4,5-diphenylin1idazo1e. 15 40 EXAMPLE 4- EXAMPLE 5 10 mg. of a copolymer of methyl methacrylate and 4 R is hydrogen, halogen, an alkyl group of 1 to 4 carbon atoms, a phenyl group, a naphthyl group or a styryl group;

or (2) an azole compound which is an imidazole group incorporated in a polymer comprising recurring units of the formula:

2. Process according to claim 1, wherein the photovinyl-imidazole comprising 28 moles percent of 4-vinylpolymerisation initiator is present in an amount within the 9 range of 0.01 to 5% by weight based on the weight of the ethylenically unsaturated organic compound present.

3. Process according to claim 1, wherein a photo-oxidation sensitizer of the class consisting of acridine, phenazine, or fiuoresceine dyes is present in the photopolymerisation composition in an amount between 0.001 and 0.1% by Weight with respect to the ethylenically unsaturated organic compound present.

4. Process according to claim 3, wherein the photopolymerisation initiator is 2,4,5-triphenyloxazole and the photo-oxidation sensitizer is euflavine.

5. Process according to claim 3, wherein the photopolymerisation initiator is 2,4,5-triphenylimidazole and the photo-oxidation sensitizer is rose bengale.

6. Process according to claim 3, wherein the photopolymerisation initiator is N-methyl-2,4,5-triphenyl-imidazole and the photo-oxidation sensitizer is rose bengale.

7. Process according to claim 3, wherein the photopolymerisation initiator is a copolymer of methyl methacrylate and 4-vinylirnidazole comprising 28 moles percent of 4-vinyl-imidazole and the photo-oxidation sensitizer is rose bengale.

References Cited UNITED STATES PATENTS 3,479,185 11/ 1969 Chambers, Jr.

FOREIGN PATENTS 1,481,819 4/1967 France 204159.23

MURRAY TILLMA'N, Primary Examiner R. B. TURER, Assistant Examiner U.S. Cl. X.R. 

